1. Field of the Invention
This invention broadly relates to electrical switch keyboards. More particularly, it concerns switch keyboards having a one-piece resilient sheet over a frame with switch elements on the frame side of the sheet so the sheet seals the entire device against any intrusion of dirt, moisture, etc. into the keyboard.
2. Description of the Prior Art
Switch keyboards are known in which keys are arranged on a frame and there is a mat so designed that, when viewed from the operating side of the keyboard, the mat covers the frame so completely that only the keys are left uncovered. For assembly, the mat is basically clamped between a first piece of the frame which contains the switch devices and a cover as a second part having corresponding openings for the keys of the switch devices. Such prior keyboards have the disadvantage of having empty spaces between the cover with the opening for the keys and the mat since dirt can gather in such spaces and cleaning away the dirt is difficult.
Other keyboard designs are known in which a resilient mat is a final coating for the frame. Such keyboards either have additional spring mechanisms and/or the keys are not guided in their reciprocation movement so that, on actuation of the keys, guidance of the keys may not be precise and there is a lack of tactile feeling by the operator of switch operation.